problems with mild steel TIG?

[FASTdan]

I'm trying to extend a tubular union made from mild steel using some plain mild steel tube, butt welded.

For some reason the weld pool is bubbling and the resulting weld has pin holes. I'm using red tip 1.6mm tungsten and about 40A. Both components were cleaned on a stainless wire wheel prior to welding.

Any suggestions as to whats going wrong?

 

[gordon stephenson]

Is it a closed tube i;e expanding air from welding heat can't escape.Looks like the air is pushing through the molten weld pooL?

 

[mike os]

are you using tig filler wire?

 

[bert]

as above, if its sealed the expanding air cant escape and will push out on the weakest point which will be the molten weld pool.

 

[Paul.]

The appearance of that weld is typical of using gas welding rods with tig, rods for tig will be stamped with the grade on a flat pressed in the end of the rod.
Also you need a bigger ceramic, the weld bead is wider than the one you are using there which is bound to give coverage problems,
venting as mentioned above is sometimes required, but usually causes problems when you close the weld rather than in the pool

 

[FASTdan]

Thanks for the replies.

It is not a closed tube - the bore is 4.5mm right through and open at both ends so air escape should not be an issue, but granted that is exactly how it is behaving. At the end of the run I get a bubble raising up too.

The behaviour occurs with or without filler wire so I'm not sure the filler is the issue? I must admit the rods I'm using are a couple of years old but Im fairly sure they came from an old place of work where they regularly TIG'd MS.

The weld is only that wide because I ground it down and welded over the top trying to cover the porosity. The original weld was 2-3mm wide (had a 2mm prep on one side of the joint). I will try a larger ceramic though just to check.

I have experimented with gas from 10 CFH to 30 CFH without much change.

 

[Paul.]

It looks to me as if that fitting is zinc plated, I assume you have cut the end off and extended it with a tube?.
Coatings will cause problems and are not easy to get rid of on a fitting because it is on the inside as well as the outside, wire brushing alone wont do it. also the material that the fitting is made from may be a free cutting grade containing lead and sulphur that is designed for machining rather than welding, its a very common cause of porosity in the welding of machined components.
To check if you have proper tig rods look at the ends, if its not stamped similar to this example then its probably not a tig rod

 

[FASTdan]

It looks to me as if that fitting is zinc plated, I assume you have cut the end off and extended it with a tube?.
Coatings will cause problems and are not easy to get rid of on a fitting because it is on the inside as well as the outside, wire brushing alone wont do it. also the material that the fitting is made from may be a free cutting grade containing lead and sulphur that is designed for machining rather than welding, its a very common cause of porosity in the welding of machined components.
To check if you have proper tig rods look at the ends, if its not stamped similar to this example then its probably not a tig rod

Yes I think you are probably right in all cases there. I guess I can run a drill through it to remove the coating on the inside, but not much I can do about the grade of material. I think my rods are gas rods - I only have a couple of part used ones left, but assuming I didnt burn them from the wrong end they are not stamped in anyway. Best go buy some proper rods for a start

Edited to add, the component is manufactured from a hex-bar if that sheds anymore light on the likely grade?

 

[FranV8]

Just a couple of things I've found (total amateur TIG person BTW)

-as Paul said, the rods will be stamped more than once on a typical welding rod, from memory it's 2-3 stamps along its length.
-I can't remember what is added to the TIG rod, I think it might be silica, but even when doing an otherwise autogenous (I. E. No filler) I often have the filler rod to hand, it can calm down a weld puddle when you find it's starting to get a bit funky.

 

[justmental]

my steel tig rods have not got stamp marks on them and the are tig rods ER70S2.